bpf: Reduce the scope of rcu_read_lock when updating fd map

There is no rcu-read-lock requirement for ops->map_fd_get_ptr() or
ops->map_fd_put_ptr(), so doesn't use rcu-read-lock for these two
callbacks.

For bpf_fd_array_map_update_elem(), accessing array->ptrs doesn't need
rcu-read-lock because array->ptrs must still be allocated. For
bpf_fd_htab_map_update_elem(), htab_map_update_elem() only requires
rcu-read-lock to be held to avoid the WARN_ON_ONCE(), so only use
rcu_read_lock() during the invocation of htab_map_update_elem().

Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20231214043010.3458072-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 5b9146fa825fdfdb943d28962b4c78f25e55ce6b..ec3bdcc6a3cfd03b62735148aed923ec83b0eb45 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2523,7 +2523,13 @@ int bpf_fd_htab_map_update_elem(struct bpf_map *map, struct file *map_file,
        if (IS_ERR(ptr))
                return PTR_ERR(ptr);
 
+       /* The htab bucket lock is always held during update operations in fd
+        * htab map, and the following rcu_read_lock() is only used to avoid
+        * the WARN_ON_ONCE in htab_map_update_elem().
+        */
+       rcu_read_lock();
        ret = htab_map_update_elem(map, key, &ptr, map_flags);
+       rcu_read_unlock();
        if (ret)
                map->ops->map_fd_put_ptr(map, ptr, false);
 

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index d63c1ed42412aa1d5fdf187ac5f71934d4dc54e1..3fcf7741146aa14893defe3adaf9b6dfef888e61 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -184,15 +184,11 @@ static int bpf_map_update_value(struct bpf_map *map, struct file *map_file,
                err = bpf_percpu_cgroup_storage_update(map, key, value,
                                                       flags);
        } else if (IS_FD_ARRAY(map)) {
-               rcu_read_lock();
                err = bpf_fd_array_map_update_elem(map, map_file, key, value,
                                                   flags);
-               rcu_read_unlock();
        } else if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) {
-               rcu_read_lock();
                err = bpf_fd_htab_map_update_elem(map, map_file, key, value,
                                                  flags);
-               rcu_read_unlock();
        } else if (map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
                /* rcu_read_lock() is not needed */
                err = bpf_fd_reuseport_array_update_elem(map, key, value,